Basics of Periodic Table Structure

Atomic Number: the number of protons in their nucleus.
Mass number: the number of nucleons (protons and neutrons) in the atomic nucleus.

Different isotopes of a given element are distinguished by their mass number, which is written as a superscript on the left hand side of the chemical symbol.

There is a total of 118 elements on the periodic table.
There are two versions of the periodic table, the 32-column or long form and the more common 18-column or medium-long form.

rows ("periods"): there are seven complete periods, Any new elements will be placed into an eighth period. All elements in a row have the same number of electron shells.
columns ("groups") (also known as a family): There are 18 numbered groups in the periodic table; the 14 f-block columns, between groups 2 and 3, are not numbered. Elements in the same group (column) have similar chemical and physical properties

In nature, only elements up to atomic number 94 exist;[a] to go further, it was necessary to synthesize new elements in the laboratory synthetic elements produced in nuclear reactions, The discovery and synthesis of further new elements is an ongoing area of scientific study.

Basics of Periodic Table Structure